The invention is generally directed to the field of disc drives and more particularly to controlling acoustic noise emissions emanating from a disc drive voice coil motor assembly.
Modern hard disc drives comprise one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks. Data is written to, and read from, the tracks via transducers (xe2x80x9cheadsxe2x80x9d) mounted to a radial actuator, which positions the heads relative to the discs.
Typically, such radial actuators employ a voice coil motor (VCM) to position the heads with respect to the disc surfaces. The heads are mounted via flexures at the ends of a plurality of arms which project radially outward from a substantially cylindrical actuator body. The actuator body pivots about a shaft mounted to the disc drive housing at a position closely adjacent the outer extreme of the discs. The pivot shaft is parallel with the axis of rotation of the spindle motor and the discs, so that the heads move in a plane parallel with the surfaces of the discs.
Normally, the VCM includes a coil mounted on the side of the actuator body opposite the head arms between an array of permanent magnets which are held above and/or below the coil on upper and/or lower magnet plates, respectively. When controlled current is passed through the coil, a magnetic field is generated. The generated electromagnetic field interacts with the magnetic field of the permanent magnets thus causing the coil to move relative to the magnets in accordance with the well-known Lorentz relationship. As the coil moves, the actuator body pivots about the pivot shaft and the heads are moved across the disc surfaces.
Typically, the heads are supported on the actuator arms in a position over the discs by actuator slider assemblies which include air-bearing surfaces designed to interact with a thin layer of moving air generated by the rotation of the discs, so that the heads may xe2x80x9cflyxe2x80x9d over the disc surfaces. Generally, the heads write data to a selected data track on the disc surface by selectively magnetizing portions of the data track through the application of a time-varying write current to the head. In order to subsequently read back the data stored on the data track, the head detects flux transitions in the magnetic fields of the data track and converts these flux transitions to a signal which is decoded by read channel circuitry of the disc drive.
A closed-loop servo system is used to control the position of the heads with respect to the disc surfaces. More particularly, during a track following mode in which a head is caused to follow a selected data track, servo information is read which provides a position error signal indicative of the position of the head relative to a center line of the track. The position error signal is used, when necessary, to generate a correction signal that in turn is provided to a power amplifier. The power amplifier then passes current through the actuator coil to adjust the position of the head relative to the track.
During a seek operation, the servo system receives the address of the destination track and generates control signals that cause the heads to initially accelerate and then subsequently decelerate as the head nears the destination track. At some point towards the end of the deceleration of the head, the servo system will transition to a settle mode during which the head is settled onto the destination track and, thereafter, the servo system causes the head to follow the destination track in a track following mode.
Generally, the objective of a typical seek operation has been to move the head from the initial track to the destination track in a minimum amount of time (access time). However, one drawback associated with rapidly moving heads to the destination track is the occurrence of mechanical vibrations excited in the upper and/or lower magnet plates during the seek operation. These vibrations may induce noise into the servo control loop of the disc drive, thus making accurate track following difficult. As will be understood, the negative affects of vibrationally induced noise in the servo system are compounded as the track density or tracks per inch (TPI) of the disc drive is increased. The general trend in the disc drive industry is to produce disc drives having ever increasing TPI. As such, it is imperative that new methods and techniques are developed to address vibrationally induced servo system noise. Additionally, these vibrations can generate excessive acoustic noise emissions from the disc drive.
Along with the general trend in the industry to provide disc drives having greater TPI, there is also a trend to reduce the level of acoustic emissions generated by disc drives. A primary source of acoustical emissions from a disc drive is the amplification of the aforementioned vibrations of the magnet plates by the top cover and by the base of the disc drive. These vibrations occurring in the magnetic plates of the voice coil motor may be transmitted to the top cover and/or the disc drive base either as sympathetic vibrations or as direct transmissions. As in any vibrating system, the magnet plates, as well as possibly the top cover and base of the disc drive, are manifested in particular modes of vibration. These modes of vibration occur in such a way that a number of elements of the system vibrate with the same frequency.
One approach to reducing the acoustical emissions from the disc drive has been to slow down the seek operation. A slowed down seek operational setting, called a quite seek, is often provided in disc drives as an optional setting. The alternative operational setting in disc drives having a quite seek setting is an operational setting commonly referred to as the performance seek, where the seek to the track occurs quickly relative to the quite seek. However, while the quite seek reduces the acoustical emissions from the disc drive, it also necessarily reduces disc drive performance. Disc drives including such quite seek operational settings are often employed in areas, such as government and private offices, that are subject to strict environmental noise limitations.
Another approach to reducing the acoustical emissions from the disc drive is to add a damping material between the upper magnetic plate and the top cover of the disc drive. For this approach to be effective, the top cover must be sufficiently rigid to provide deflection of the damping material. However, the stiffness required for this approach to be useful often adds unacceptable weight and manufacturing costs to the disc drive. Additionally, comparative tests indicated that placing the damping material between the upper magnet plate and the top cover is not as effective as other methods, including the methods described with respect to the present invention.
Another approach to reducing the acoustical emissions from the disc drive involves securing the upper magnet plate to the top cover of the disc drive, either directly or with an intermediary damping material positioned between the upper magnetic plate and the top cover of the disc drive. This approach, however, has proven to be ineffective in disc drives employing light weight or relatively thin top covers where the top cover tends to behave like a speaker cone amplifying the vibrations from the coupled upper magnetic plate.
Accordingly there is a need for a disc drive damping system and/or method which effectively reduces VCM vibrations in a disc drive and, thereby, reduces acoustical emissions and vibrationally induced noise in the disc drive""s servo system.
Against this backdrop various embodiments of the present invention has been developed. In general, the various embodiments of the present invention relate to systems and methods of minimizing vibrationally induced noise in a disc drive servo system. Additionally, embodiments of the present invention relate to reducing vibrationally induced acoustical emissions from a disc drive device.
One embodiment of the present invention relates to a disc drive including a base plate having an upper surface, a voice coil motor operably attached to the upper surface of the base plate, and a damper pad positioned on the upper surface of the base plate between the base plate and the voice coil motor for damping vibrations occurring in the base plate and/or the voice coil motor.
Another embodiment relates to a disc drive including a base plate having an upper surface, a voice coil motor operably attached to the upper surface of the base plate, wherein the voice coil motor has a lower magnetic plate that is spaced from the upper surface of the base plate. A damper pad is preferably positioned on the upper surface of the base plate between the base plate and the lower magnetic plate such that vibrations occurring in the base plate and both the lower magnet plate and upper magnet plate are dampened.
Additionally, yet another embodiment relates to a disc drive damping system comprising a disc drive having a base plate and a voice coil motor connected to the base plate and a damping means positioned between the voice coil motor and the base plate for damping vibrations in the disc drive.
These and various other features as well as advantages which characterize the various embodiments of the present invention will be apparent from a reading of the following detailed description, a review of the associated drawings, and the appended claims.